PROJECTSUMMARY FoodallergyisincreasinglyprevalentintheUnitedStates,andapproximatelyone-thirdofpatientshave reactivitytomultiplefoods.Thereisanunmetclinicalneedtotreatmulti-foodallergyinatimelyandefficacious manner,butthemechanisticfactorsthatshouldguideselectionofanoptimaltreatmentstrategyareunclear. ThisprojectaimstoobtainfundamentalnewunderstandingofhumanBcellandimmunoglobulin(Ig) responsesinpatientsallergictomultiplefoods,andtoanalyzetheBcellalterationsinducedbymulti-allergen oralimmunotherapy(multi-OIT)aloneorincombinationwithbiologicstargetingIgEortheIL-4/IL-13receptor componentIL-4R?.Wewilluseflowcytometryisolationofallergen-specificBcells,focusingoncellsspecific formilk,peanutorcashewallergens,pairedwithDNAdeepsequencingofimmunoglobulin(Ig)gene rearrangements,tocharacterizepathogenicBcellpopulationsinallergicpatients,andtodeterminewhat changesinclonalpopulations,antibodyisotypeexpression,antibodysomaticmutation,andaffinityareinduced intheseBcellpopulationsduringsuccessfulmulti-OITtreatment.WewillevaluatewhetherthereareBcell repertoirefeatures,eitherpriortomulti-OIT,orduringmulti-OIT,thatpredictparticipants?responsesandcould beusedtoguidetherapy.Thestudieswillbeperformedonspecimensfromwell-characterizedmulti-allergic participantsinthepilot,phase2multi-OITclinicaltrialproposedinProject1,aswellasfromappropriate atopicandhealthycontrolsubjects.WewillevaluateandcomparethemolecularfeaturesofBcellsand antibodiesspecificformilk,peanutandcashewallergens,andtheiralterationsinresponsetomulti-OIT,within thesamepeople.Inasubsetofparticipants,wewillstudyBcellsinbothbloodandGIbiopsyspecimens,to determinetowhatextentperipheralbloodBcellmonitoringaccuratelyreflectstheallergicdiseasestateinthe GItractofpatients,andthechangesinducedbymulti-OIT.Importantly,wewillalsoanalyzetheeffectsof monoclonalantibodytherapiestargetingIgEorIL-4R?duringmulti-OIT,todeterminetheextenttowhichthese biologictherapiesaffectthenatureandtimecourseofBcellchangesinducedbymulti-OIT.Wewilladditionally performlong-termfollowupstudiesofBcellsinparticipantsinourPOISEDandMAPXOITtrials. TheBcelldatafromthisProjectwillbecombinedandanalyzedtogetherwithclinicaldataandexperimental datafromTcellsandbasophilsfromProjects1,3and4,andCoreB,incollaborationwiththeDataAnalysis CoreC,toenableacomprehensiveevaluationofimmunologicalphenotypesassociatedwithmulti-food allergicdisease,andwithsuccessfulanddurabletherapeuticresponsestomulti-OIT.